The present invention relates to a textile machine and the control method thereof.
It is known that in textile machines such as needle looms, among which also the crocheting machines are included, formation of the textile product takes place by mutual interlacing, following predetermined patterns, of a plurality of warp and weft yarns, suitably engaged by respective weaving or knitting members; the latter are for example the healds mounted on one or more heald frames, a predetermined number of sickles and at least one needle.
Also present are auxiliary members such as weft-yarn knocking-over devices and compacting reeds.
These weaving members are operated, through appropriate actuators or kinematic mechanisms of the mechanical type, through synchronized cyclic movements to cause mutual intertwining of the warp yarns and weft yarns following the desired knitting pattern.
The weft yarns are fed to the respective weaving members by a plurality of bobbins mounted on a rack-shaped structure called “unwinding creel”, while the warp yarns are unwound from a plurality of beams supported by a beam-carrying unwinding creel.
It is also provided that appropriate take-down rollers should cause sliding of the textile product and progressive supply of same to the machine exit.
The bobbins on which the weft yarns are wound are free to rotate about their longitudinal rotation axis, and the tension with which the weft yarns are fed to the respective sickles is determined by the rotation speed of the rollers that are interposed between the bobbins and the sickles and are disposed close to each other so as to engage the weft yarns.
Rotation of these rollers is usually caused by a kinematic connection between said rollers and the main shaft of the textile machine; since this connection is of a purely mechanical type, it keeps a fixed position during production of the whole fabric.
Therefore, each sickle always receives the same amount of weft yarn in a time unit and, to vary this amount, the machine is to be stopped and the kinematic connection ratios between the main shaft and said rollers are to be modified.
Likewise, the warp yarns too are fed to the healds through rollers disposed suitably close to each other and the finished product is picked up from the machine by a quite similar roller member.
Both the warp yarn feeding member and the textile-product take-down member are mechanically connected with the main shaft, so that the follow-up ratio (i.e. the ratio between the number of revolutions carried out in the time unit by the feeding/take-down rollers and the number of revolutions carried out in the time unit by the main shaft) keeps constant over the whole working of the textile product.
Consequently, it is not possible to alter tensioning of the weft and warp yarns when supplied to the respective bars without stopping operation of the machine, neither is it possible to modify the pulling tension applied when the finished product is removed from the machine.
Therefore, by adopting these modalities of use of the loom it is not possible to alter the fabric compactness or density both in a transverse direction and in a direction parallel to the extension of the textile product, without stopping operation of the machine.
In addition, exactly due to the fact that the warp and weft yarns are fed to the healds and sickles respectively at a constant tension and the textile product is caused to slide between the take-down rollers at a constant tension in time, it is not possible to obtain particular aesthetic effects through a controlled variation of the fabric compactness, without stopping operation of the machine, said aesthetic effects comprising alternations of thinner and more compact regions, narrowing or shrinkage of the textile product along a direction substantially perpendicular to the movement direction in which the textile product itself is moved by the take-down rollers, etc.